* Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University, Boston, MA. ** Department of Kinesiology, University of Maryland, College Park, MD. *** Department of Health Sciences, Boston University Sargent College of Health and Rehabilitation Sciences, Boston, MA. **** Nutrition, Metabolism and Exercise Unit, Department of Geriatrics, University of Arkansas for Medical Sciences, Little Rock, AR. ***** School of Nutrition, Science and Policy, Tufts University, Medford, MA. This material is based upon work supported by the U.S. Department of Agriculture, under agreement No. 58-1950-9-001, and the National Institute on Aging contract AG 1181. Any opinions, findings, conclusion, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture. Correspondence: Carmen Castaneda, M.D., Ph.D., Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University, 711 Washington St., Boston MA 02111. Telephone number (617) 556-3081. Fax number: (617) 556-3083. E-mail: ccastaneda@hnrc.tufts.edu

Abstract: We investigated the effects of dietary protein on plasma IGF-I levels and muscle fiber cross-sectional area (CSA). Twelve healthy elderly women were randomly assigned to a weight-maintaining diet containing either 1.47 (marginal) or 2.94 (adequate) g protein/kg body cell mass (BCM)/d, (0.45 and 0.92 g/kg body weight/d, respectively) for 10wks. Plasma IGF-I levels and muscle fiber areas and distributions were evaluated at baseline and 10wks. After 10wks, both IGF-I and type I fiber CSA had declined significantly in subjects fed the marginal diet (30.1±2.1% and 32.7±7.9%, respectively) while they increased in those fed the adequate diet (19.5±7.0% and 22.3±7.5%, for IGF-I and type I CSA, respectively). The change in IGF-I was the only significantly associated with the change in type I fiber CSA (r2=0.70; p<0.03). These findings show that marginal dietary protein intakes will result in losses of muscle mass in the elderly and suggest a role for plasma IGF-I as a biochemical marker for the histological changes in skeletal muscle. Journ. of Nutr. Health & Aging 2000; 4 (2): 85-90

Key words: aging, accommodation, protein status, muscle atrophy